Method for preparing carbon nanotube/polymer composite

ABSTRACT

Provided is a method for preparing a carbon nanotube/polymer composite material, including: coating a nano-silicon oxide film on the surface of a porous polymer by vacuum coating; depositing a metal catalyst nano-film on the nano-silicon oxide film by vacuum sputtering; growing a carbon nanotube array in situ on the surface of the porous polymer by plasma enhanced chemical vapor deposition to obtain a carbon nanotube/polymer porous material; and impregnating the carbon nanotube/polymer porous material with a polymer and curing to obtain the carbon nanotube/polymer composite material. By using a heat-resistant polymer having a high heat-resistant temperature and a PECVD technique, a carbon nanotube array directly grows in situ on the surface of a polymer at a low temperature, which thereby overcomes the defects of the composites previously prepared, in which carbon nanotubes are difficult to be homogeneously dispersed and the interfacial bonding force in the composites is weak.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Chinese Patent Application No.201810355067.5, filed on Apr. 19, 2018, and the disclosure of which ishereby incorporated by reference.

FIELD

The present invention relates to the technical field of carbonnanotubes, and in particular to a method for preparing a carbonnanotube/polymer composite material.

BACKGROUND

Since carbon nanotubes were discovered in 1991, they have had manypotential application values in the future high-tech fields such asnano-electronic devices and hydrogen storage fuel cells, etc., due totheir unusual mechanical, electrical, thermal and other properties aswell as their unique quasi-one-dimensional tubular molecular structures.The carbon nanotube can be regarded as being obtained by curlingtwo-dimensional graphene to a closed state, and its desired structure isa seamless and hollow tube which is bounded by hexagonal lattices ofcarbon atoms and has two ends being covered by hemispherical largefullerene molecules. The tube wall of a carbon nanotube is composed ofsix-membered rings of carbon, wherein carbon atoms in each of thesix-membered rings are mainly SP² hybridized, and each of the carbonatoms forms a carbon-carbon σ bond by overlapping its SP² hybrid orbitalwith the SP² hybrid orbital of a carbon atom on an adjacent six-memberedring. Due to the formation of a spatial structure, the SP² hybridorbital is deformed, which leads to the formation of a hybrid structurebetween SP² and SP³.

Carbon nanotubes have excellent mechanical properties, an extremelylarge aspect ratio, good electrical properties, and very high chemicaland thermal stability, etc., and both theoretical and experimentalstudies have shown that the carbon nanotubes can be used to prepare apolymer-based composite with excellent properties, and can impart thecomposite with good strength, elasticity, fatigue resistance andisotropism, which dramatically improves the mechanical properties of thecomposite. Meanwhile, the carbon nanotubes have good heat transferproperties and extremely high axial thermal conductivity, andexperimental results have shown that the thermal conductivity ofindividual SWCNTs is up to 6000 W/(wK), and thus the carbon nanotubesare widely used to prepare thermally conductive composites. A polymerhas advantages of light mass, corrosion resistance and radiationresistance, etc., such that the polymer can be applied in novelspacecrafts, however, its poor mechanical and thermal conductiveproperties limit the application range thereof, and thus manyresearchers have improved the mechanical and thermal conductiveproperties of the polymer by adding a carbon nano-material such asgraphene, carbon nanotubes. All the existing polymer-carbon nanotubecomposites are prepared by using carbon nanotubes as a filler and mixingwith a polymer precursor to thereby prepare carbon nanotube/polymercomposite materials. This method is simple, but still has somedrawbacks. For example, the carbon nanotubes have poor dispersibility inthe polymer and are susceptible to agglomeration; and improvement ininterfacial bonding between the carbon nanotubes and the polymer isneeded, etc. Meanwhile, in order to form good bonding between thepolymer and the carbon nanotubes, it is usually necessary to decorateand modify the surface of the carbon nanotubes to thereby improve theprocessability thereof, enhance the compatibility between the carbonnanotubes and the polymer, and increase the dispersibility of the carbonnanotubes. However, such surface decoration and modification of thecarbon nanotubes will increase the defects of the carbon nanotubes,resulting in a significant decrease in thermal conductive and mechanicalproperties, which will seriously affect the comprehensive properties ofthe composite. Therefore, the existing techniques cannot satisfy thepreparation of a carbon nanotube-polymer composite having high quality,high dispersibility, and high interfacial bonding.

SUMMARY

In view of this, the technical problem to be solved by the presentinvention is to provide a preparation method of a carbonnanotube/polymer composite material with high strength and thermalconductivity.

The present invention provides a preparation method of a carbonnanotube/polymer composite material, comprising the steps of:

coating a nano-silicon oxide film on the surface of a porous polymer byvacuum coating;

depositing a metal catalyst nano-film on the nano-silicon oxide film byvacuum sputtering;

growing a carbon nanotube array in situ on the surface of the porouspolymer by plasma enhanced chemical vapor deposition to obtain a carbonnanotube/polymer porous material; and

impregnating the carbon nanotube/polymer porous material with a polymerand curing to obtain the carbon nanotube/polymer composite material.

Preferably, the porous polymer is prepared by:

subjecting a polymer monomer solution to electrostatic spinning orfreeze-drying to obtain the porous polymer.

Preferably, the polymer is selected from the group consisting ofpolyimide, phenolic resin, epoxy resin, polybenzimidazole and polyamide,or a mixture thereof.

Preferably, the nano-silicon oxide film has a thickness of 5˜50 nm, andthe metal catalyst nano-film has a thickness of 1˜10 nm.

Preferably, the metal catalyst nano-film is selected from the groupconsisting of nickel, iron and cobalt, or a mixture thereof.

Preferably, the growing of the carbon nanotube array in situ is carriedout at a temperature of 200˜450° C. and under a pressure of 5˜20 Pa.

Preferably, the growing a carbon nanotube array in situ is carried outunder the following conditions: H₂ as a carrier gas, ethyne or methaneas a carbon source, a plasma power of 10˜500 W, and a growing durationof 5˜60 min.

Preferably, the impregnating with a polymer is carried out under vacuum.

In the present invention, a carbon nanotube/polymer composite materialwith high strength and high thermal conductive properties is preparedby: preparing a polymer in a form of a porous block material byelectrostatic spinning and freeze-drying; depositing a substrate and acatalyst on the surface of the polymer by vacuum coating and vacuumsputtering techniques; and then, by means of a PECVD technique, growingcarbon nanotubes in situ on the surface of the polymer by a plasmaenhanced deposition technique under the conditions of low temperatureand negative pressure; and finally subjecting to enclosing anddensification. In the resulting composite, the carbon nanotubes aregrown uniformly on the surface of the porous structure of the polymer,which allows the carbon nanotubes and the polymer to bond well with eachother, and meanwhile, the in situ growth technique of the array ofcarbon nanotubes allows the carbon nanotubes to be distributed uniformlywithin the pores of the composite without non-uniform dispersion andagglomeration problems, resulting in that the composite has excellentmechanical and thermal conductive properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of steps of a preparation method ofthe present invention;

FIG. 2 is a scanning electron micrograph of a porous polyimide preparedin the present invention;

FIG. 3 is a scanning electron micrograph of a catalyst-supportedpolyimide prepared in the present invention;

FIG. 4 is a scanning electron micrograph of a composite with in situgrown carbon nanotubes prepared in the present invention; and

FIG. 5 is a scanning electron micrograph of an enclosed compositeprepared in the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention provides a preparation method of a carbonnanotube/polymer composite material, comprising the steps of:

coating a nano-silicon oxide film on the surface of a porous polymer byvacuum coating;

depositing a metal catalyst nano-film on the nano-silicon oxide film byvacuum sputtering;

growing a carbon nanotube array in situ on the surface of the porouspolymer by plasma enhanced chemical vapor deposition to obtain a carbonnanotube/polymer porous material; and

impregnating the carbon nanotube/polymer porous material with a polymerand curing to obtain the carbon nanotube/polymer composite material.

The polymer of the polymer is selected from the group consisting ofpolyimide, phenolic resin, epoxy resin, polybenzimidazole and polyamide,or a mixture thereof.

The above porous polymer is preferably prepared by:

subjecting a polymer monomer solution to electrostatic spinning orfreeze-drying to obtain the porous polymer.

The solvent for the polymer monomer solution can be selected accordingto the type of the polymer, and is preferably dimethyl acetamide (DMAC)or N-methyl pyrrolidone (NMP).

When the polymerization and curing of the polymer are difficult, acuring agent and/or an accelerator can be added into the solution of thepolymer, and the type of the curing agent and accelerator can beapplicable ones which are well known to those skilled in the art.

The polymer monomer solution preferably has a solid content of 10%˜30%.

Then, a porous polymer fibrous mat can be prepared by an electrostaticspinning technique; or alternatively, a porous polymer material can beobtained using a freeze-drying technique in which a prepared polymerslurry is freeze-dried in liquid nitrogen, removed for the solventtherefrom and finally curing, either of which is used as a skeletalstructure of the composite.

Thereafter, a layer of silicon oxide film with a nano-scaled thickness,referred to as a nano-silicon oxide film, is coated on the surface ofthe porous polymer by a vacuum coating technique, which serves as asubstrate for growing carbon nanotubes. The silicon oxide film issupported on the surface of the polymer and the pores thereof.

The nano-silicon oxide film preferably has a thickness of 5˜50 nm.

Next, a layer of metal catalyst nano-film with a nano-scaled thickness,referred to as a metal catalyst nano-film, is sputtered and deposited onthe nano-silicon oxide film by vacuum sputtering, which serves as acatalyst for growing a carbon nanotube array.

The metal catalyst nano-film is preferably of one or more of metals suchas nickel, iron, and cobalt.

The metal catalyst nano-film preferably has a thickness of 1˜10 nm.

Subsequently, a carbon nanotube array is grown in situ on the surface ofthe metal catalyst nano-film by a plasma enhanced chemical vapordeposition (PECVD) process, to obtain a carbon nanotube/polymer porouscomposite.

Specifically, a metal catalyst-supported porous polymer is placed into aPECVD furnace, and vacuum is applied thereto to form a negative pressurewithin the furnace tube such that the pressure is preferably 5˜20 Pa.Then, H₂ is introduced as a carrier gas, preferably at a flow rate of10˜100 sccm. Preferably, when the temperature is raised up to 200˜450°C., a radio-frequency plasma emitter is turned on, preferably with theradio-frequency power set at 10˜500 W and the radio-frequency signalfrequency set at 13.56 MHz. Preferably, after treatment under the H₂plasma environment for 5˜30 min, ethyne or methane is introduced as acarbon source for growing carbon nanotubes, preferably at a flow rate of10˜80 sccm, during which different flow rate ratios between H2 and theethyne or methane are adjusted, with the growth time being preferably5-60 min. After the reaction is completed, the plasma emitter is turnedoff, and the resultant is cooled to room temperature along with thefurnace under the H₂ atmosphere environment.

The above temperature is lower than the maximum service temperature ofthe polymer, and thus the polymer does not undergo high temperaturepyrolysis.

Finally, the grown carbon nanotube/polymer porous composite isimpregnated with corresponding monomers for the polymer with the aid ofvacuum, and then subjected to polymerization and curing processes toimmobilize the carbon nanotubes and fill the pores such that the poresbetween the carbon nanotubes are enclosed, and by several impregnationand curing processes above, a dense carbon nanotube/polymer compositematerial is obtained.

Unlike the composites prepared by a blending process which is currentlygenerally used, a microscopically ordered composite prepared by growinga carbon nanotube array in situ on the surface of a polymer in thepresent invention can realize directional and high-efficiency thermalconduction and mechanical enhancement, which creates a novel method forpreparing an ordered carbon/polymer composite. Using a heat-resistantpolymer having a high heat-resistant temperature and a PECVD technique,a carbon nanotube array can be grown at a low temperature such that thecarbon nanotubes are directly grown in situ on the surface of a polymerto prepare a composite, which thereby overcomes the defects that in thecomposites previously prepared, carbon nanotubes are difficult to beuniformly dispersed and the interfacial bonding force in the compositesis poor, creating a novel technique utilizing an ordered compositestructure to improve the directional thermal conduction and strengthproperties of the composite.

Hereinafter, the preparation method of a carbon nanotube/polymercomposite material of the present invention will be described in detailin combination with examples in order to further illustrate the presentinvention.

EXAMPLE 1

(1) 3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA) and4,4′-oxydianiline (ODA) were weighed in a molar ratio of 1:1, dissolvedin dimethyl acetamide (DMAC), and reacted at 0° C. for 5 hours. Then,1,3,5-triaminophenoxy benzene (TAB) was added thereto to performchemical crosslinking, to obtain a polyamic acid (PAA) stock solutionwith a solid content of 15%. Subsequently, a fibrous mat of an oligomerwas prepared by an electrostatic spinning technique, and finallysubjected to imidization at 350° C. to obtain a porous polyimide fibrousmat. A scanning electron micrograph of the porous polyimide is shown inFIG. 2.

(2) The prepared porous polyimide material was coated on its surfacewith a layer of silicon oxide film having a thickness of 10 nm by avacuum coating technique. Then, a layer of nickel (or iron, cobalt) thinfilm having a thickness of 2 nm was sputtered on the polyimide by vacuumsputtering, which was used as a catalyst for growing carbon nanotubes. Ascanning electron micrograph of the prepared catalyst-supportedpolyimide material is shown in FIG. 3.

(3) The catalyst-supported porous polyimide was placed into a PECVDfurnace, and vacuum was applied thereto such that the pressure in thefurnace tube was 5˜20 Pa. Then, H₂ was introduced as a carrier gas at aflow rate of 100 sccm. When the temperature was raised up to 300° C., aradio-frequency plasma emitter was turned on, with the radio-frequencypower set at 200 W and the radio-frequency signal frequency set at 13.56MHz. After treatment under the H₂ plasma environment for 30 min, ethynewas introduced at a flow rate of 20 sccm as a carbon source for growingcarbon nanotubes, to grow carbon nanotubes for a period of 15 min. Afterthe reaction was completed, the plasma emitter was turned off, and theresultant was cooled to room temperature along with the furnace underthe H₂ atmosphere environment, to obtain a polyimide with a grown arrayof carbon nanotubes. A scanning electron micrograph of the abovecomposite with in situ grown carbon nanotubes is shown in FIG. 4.

(4) The porous composite with grown carbon nanotubes was impregnatedwith a polyamic acid solution and subjected to thermal imidization at350° C. Such an operation was repeated several times and thus thecomposite was densified, to finally obtain a dense carbonnanotube/polyimide composite. A scanning electron micrograph of theenclosed composite is shown in FIG. 5.

The resulting carbon nanotube/polyimide composite had a mass fraction ofcarbon nanotubes of 6.5 wt %, had excellent mechanical properties andthermal conductivity, and had a tensile breaking strength of up to 410MPa, a tensile modulus of 3.2 GPa and a coefficient of thermalconductivity of 13 W/mK.

EXAMPLE 2

(1) 3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA) and4,4′-oxydianiline (ODA) were weighed in a molar ratio of 1:1, dissolvedin dimethyl acetamide (DMAC), and reacted at 0° C. for 5 hours. Then,1,3,5-triaminophenoxy benzene (TAB) was added thereto to performchemical crosslinking, to obtain a polyamic acid (PAA) stock solutionwith a solid content of 15%. Subsequently, using a freeze-dryingtechnique, the prepared gel was freeze-dried in liquid nitrogen, removedfor the solvent therefrom using the freeze-drying technique, and finallysubjected to imidization at 350° C. to obtain a porous polyimidematerial.

(2) The prepared porous polyimide material was coated on its surfacewith a layer of silicon oxide film having a thickness of 20 nm by avacuum coating technique. Then, a layer of nickel (or iron, cobalt) thinfilm having a thickness of 10 nm was sputtered on the polyimide byvacuum sputtering, which was used as a catalyst for growing carbonnanotubes.

(3) The catalyst-supported porous polyimide was placed into a PECVDfurnace, and vacuum was applied thereto such that the pressure in thefurnace tube was 5˜20 Pa. Then, H₂ was introduced as a carrier gas at aflow rate of 50 sccm. When the temperature was raised up to 450° C., aradio-frequency plasma emitter was turned on, with the radio-frequencypower set at 100 W and the radio-frequency signal frequency set at 13.56MHz. After treatment under the H₂ plasma environment for 30 min, ethynewas introduced at a flow rate of 50 sccm as a carbon source for growingcarbon nanotubes, to grow carbon nanotubes for a period of 30 min. Afterthe reaction was completed, the plasma emitter was turned off, and theresultant was cooled to room temperature along with the furnace underthe H₂ atmosphere environment.

(4) The porous composite with grown carbon nanotubes was impregnatedwith a polyamic acid solution and subjected to thermal imidization at350° C. Such an operation was repeated several times and thus thecomposite was densified, to finally obtain a dense carbonnanotube/polyimide composite.

The resulting carbon nanotube/polyimide composite had a mass fraction ofcarbon nanotubes of 8.2 wt %, had excellent mechanical properties andthermal conductivity, and had a tensile breaking strength of up to 479MPa, a tensile modulus of 4.13 GPa and a coefficient of thermalconductivity of 17.3 W/mK.

EXAMPLE 3

(1) An epoxy resin (E-03, having an epoxide number of 0.00˜0.04) wasdissolved in 1-methoxy-2-propanol (MP) at room temperature, and stirredfor 30 min to allow sufficient dissolution of the epoxy resin, toformulate an epoxy resin solution at a concentration of 30%. Then, afibrous mat of the epoxy resin was prepared by an electrostatic spinningtechnique.

(2) The prepared porous epoxy resin material was coated on its surfacewith a layer of silicon oxide film having a thickness of 10 nm by avacuum coating technique. Then, a layer of nickel (or iron, cobalt) thinfilm having a thickness of 10 nm was sputtered on the epoxy resin byvacuum sputtering, which was used as a catalyst for growing carbonnanotubes.

(3) The catalyst-supported porous epoxy resin was placed into a PECVDfurnace, and vacuum was applied thereto such that the pressure in thefurnace tube was 5-20 Pa. Then, H₂ was introduced as a carrier gas at aflow rate of 100 sccm. When the temperature was raised up to 200° C., aradio-frequency plasma emitter was turned on, with the radio-frequencypower set at 300 W and the radio-frequency signal frequency set at 13.56MHz. After treatment under the H₂ plasma environment for 10 min, ethynewas introduced at a flow rate of 10 sccm as a carbon source for growingcarbon nanotubes, to grow carbon nanotubes for a period of 20 min. Afterthe reaction was completed, the plasma emitter was turned off, and theresultant was cooled to room temperature along with the furnace underthe H₂ atmosphere environment.

(4) The porous composite with grown carbon nanotubes was impregnatedwith an epoxy resin solution and cured in a vacuum oven at 100° C. Suchan operation was repeated several times and thus the composite wasdensified, to finally obtain a dense carbon nanotube/epoxy resincomposite.

The resulting carbon nanotube/epoxy resin composite had a mass fractionof carbon nanotubes of 5.5 wt %, had excellent mechanical properties andthermal conductivity, and had a tensile breaking strength of up to 32.2MPa, a tensile modulus of 3.1 GPa and a coefficient of thermalconductivity of 9.8 W/mK.

EXAMPLE 4

(1) An epoxy resin (E-03, having an epoxide number of 0.00˜0.04) wasdissolved in 1-methoxy-2-propanol (MP) at room temperature, and stirredfor 30 min to allow sufficient dissolution of the epoxy resin, toformulate an epoxy resin solution at a concentration of 20%. Then, afibrous mat of the epoxy resin was prepared by an electrostatic spinningtechnique.

(2) The prepared porous epoxy resin material was coated on its surfacewith a layer of silicon oxide film having a thickness of 10 nm by avacuum coating technique. Then, a layer of nickel (or iron, cobalt) thinfilm having a thickness of 5 nm was sputtered on the epoxy resin byvacuum sputtering, which was used as a catalyst for growing carbonnanotubes.

(3) The catalyst-supported porous epoxy resin was placed into a PECVDfurnace, and vacuum was applied thereto such that the pressure in thefurnace tube was 5˜20 Pa. Then, H₂ was introduced as a carrier gas at aflow rate of 100 sccm. When the temperature was raised up to 150° C., aradio-frequency plasma emitter was turned on, with the radio-frequencypower set at 300 W and the radio-frequency signal frequency set at 13.56MHz. After treatment under the H₂ plasma environment for 10 min, ethynewas introduced at a flow rate of 20 sccm as a carbon source for growingcarbon nanotubes, to grow carbon nanotubes for a period of 30 min. Afterthe reaction was completed, the plasma emitter was turned off, and theresultant was cooled to room temperature along with the furnace underthe H₂ atmosphere environment.

(4) The porous composite with grown carbon nanotubes was impregnatedwith an epoxy resin solution and cured in a vacuum oven at 100° C. Suchan operation was repeated several times and thus the composite wasdensified, to finally obtain a dense carbon nanotube/epoxy resincomposite.

The resulting carbon nanotube/epoxy resin composite had a mass fractionof carbon nanotubes of 6.2 wt %, had excellent mechanical properties andthermal conductivity, and had a tensile breaking strength of up to 35.1MPa, a tensile modulus of 3.5 GPa and a coefficient of thermalconductivity of 10.2 W/mK.

EXAMPLE 5

(1) A phenolic resin and polyvinyl butyral (PVB) were dissolved inethanol in which a mass ratio of the phenolic resin, PVB, and ethanolwas 40:0.5:55.5, and stirred for 2 hours to be mixed homogeneously, toobtain a phenolic resin solution. Subsequently, an as-spun fibrous matof the phenolic resin was prepared by an electrostatic spinningtechnique, which was finally cured at 180° C. to obtain a porous fibrousmat of the phenolic resin.

(2) The prepared porous phenolic resin material was coated on itssurface with a layer of silicon oxide film having a thickness of 20 nmby a vacuum coating technique. Then, a layer of nickel (or iron, cobalt)thin film having a thickness of 2 nm was sputtered on the phenolic resinby vacuum sputtering, which was used as a catalyst for growing carbonnanotubes.

(3) The catalyst-supported porous phenolic resin was placed into a PECVDfurnace, and vacuum was applied thereto such that the pressure in thefurnace tube was 5˜20 Pa. Then, H₂ was introduced as a carrier gas at aflow rate of 10 sccm. When the temperature was raised up to 200° C., aradio-frequency plasma emitter was turned on, with the radio-frequencypower set at 500 W and the radio-frequency signal frequency set at 13.56MHz. After treatment under the H₂ plasma environment for 30 min, ethynewas introduced at a flow rate of 20 sccm as a carbon source for growingcarbon nanotubes, to grow carbon nanotubes for a period of 60 min. Afterthe reaction was completed, the plasma emitter was turned off, and theresultant was cooled to room temperature along with the furnace underthe H₂ atmosphere environment.

(4) The porous material with grown carbon nanotubes was impregnated witha phenolic resin solution and cured at 180° C. Such an operation wasrepeated several times and thus the composite was densified, to finallyobtain a dense carbon nanotube/phenolic resin composite.

The resulting carbon nanotube/phenolic resin composite had a massfraction of carbon nanotubes of 8.1 wt %, had excellent mechanicalproperties and thermal conductivity, and had a tensile breaking strengthof up to 235.1 MPa, a tensile modulus of 7.5 GPa and a coefficient ofthermal conductivity of 19.8 W/mK.

EXAMPLE 6

(1) A phenolic resin and polyvinyl butyral (PVB) were dissolved inethanol in which a mass ratio of the phenolic resin, PVB, and ethanolwas 40:0.5:55.5, and stirred for 2 hours to be mixed homogeneously, toobtain a phenolic resin solution. Subsequently, an as-spun fibrous matof the phenolic resin was prepared by an electrostatic spinningtechnique, which was finally cured at 180° C. to obtain a porous fibrousmat of the phenolic resin.

(2) The prepared porous phenolic resin material was coated on itssurface with a layer of silicon oxide film having a thickness of 50 nmby a vacuum coating technique. Then, a layer of nickel (or iron, cobalt)thin film having a thickness of 1 nm was sputtered on the phenolic resinby vacuum sputtering, which was used as a catalyst for growing carbonnanotubes.

(3) The catalyst-supported porous phenolic resin was placed into a PECVDfurnace, and vacuum was applied thereto such that the pressure in thefurnace tube was 5˜20 Pa. Then, H₂ was introduced as a carrier gas at aflow rate of 10 sccm. When the temperature was raised up to 150° C., aradio-frequency plasma emitter was turned on, with the radio-frequencypower set at 300 W and the radio-frequency signal frequency set at 13.56MHz. After treatment under the H₂ plasma environment for 30 min, ethynewas introduced at a flow rate of 20 sccm as a carbon source for growingcarbon nanotubes, to grow carbon nanotubes for a period of 30 min. Afterthe reaction was completed, the plasma emitter was turned off, and theresultant was cooled to room temperature along with the furnace underthe H₂ atmosphere environment.

(4) The porous material with grown carbon nanotubes was impregnated witha phenolic resin solution and cured at 180° C. Such an operation wasrepeated several times and thus the composite was densified, to finallyobtain a dense carbon nanotube/phenolic resin composite.

The resulting carbon nanotube/phenolic resin composite had a massfraction of carbon nanotubes of 7.2 wt %, had excellent mechanicalproperties and thermal conductivity, and had a tensile breaking strengthof up to 185.8 MPa, a tensile modulus of 6.1 GPa and a coefficient ofthermal conductivity of 18.2 W/mK.

As can be seen from the above examples, a carbon nanotube/polymercomposite material is prepared in the present invention, which hasexcellent mechanical properties and thermal conductivity.

The foregoing description of the examples is provided merely to helpunderstanding the method of the present invention and the core ideathereof. It should be pointed out that those skilled in the art can alsomake several improvements and modifications without departing from theprinciple of the present invention, and these improvements andmodifications also fall within the scope of protection of the claims ofthe present invention.

1. A method for preparing a carbon nanotube/polymer composite material,comprising: coating a nano-silicon oxide film on the surface of a porouspolymer by vacuum coating; depositing a metal catalyst nano-film on thenano-silicon oxide film by vacuum sputtering; growing a carbon nanotubearray in situ on the surface of the porous polymer by plasma enhancedchemical vapor deposition to obtain a carbon nanotube/polymer porousmaterial; and impregnating the carbon nanotube/polymer porous materialwith a polymer and curing to obtain the carbon nanotube/polymercomposite material.
 2. The method according to claim 1, wherein theporous polymer is prepared by: subjecting a polymer monomer solution toelectrostatic spinning or freeze-drying to obtain the porous polymer. 3.The method according to claim 1, wherein the polymer is selected fromthe group consisting of polyimide, phenolic resin, epoxy resin,polybenzimidazole and polyamide, or a mixture thereof.
 4. The methodaccording to claim 1, wherein the thickness of the nano-silicon oxidefilm is 5˜50 nm, and the thickness of the metal catalyst nano-film is1˜10 nm.
 5. The method according to claim 1, wherein the metal catalystnano-film is selected from the group consisting of nickel, iron andcobalt, or a mixture thereof.
 6. The method according to claim 1,wherein the growing of the carbon nanotube array in situ is carried outat a temperature of 200˜450° C. and under a pressure of 5˜20 Pa.
 7. Themethod according to claim 1, wherein the growing of the carbon nanotubearray in situ is carried out under the following conditions: H₂ as acarrier gas, ethyne or methane as a carbon source, a plasma power of10˜500 W, and a growing duration of 5˜60 min.
 8. The method according toclaim 1, wherein the impregnating with a polymer is carried out undervacuum.